Properties of the exciting source of the outflow in iras 20231+3440 region
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Cited by 3 publications
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Context. In high-mass (≥7 M ) star formation (SF) studies, high-angular resolution is crucial for resolving individual protostellar outflows (and possibly accretion disks) from the complex contribution of nearby (high-and low-mass) young stellar objects (YSO). Previous interferometric studies have focused mainly on single objects. Aims. A sensitive survey at high angular resolution is required to investigate outflow processes in a statistically significant sample of high-mass YSOs and on spatial scales relevant to testing theories. Methods. We selected a sample of 40 high-mass YSOs from water masers observed within the BeSSeL Survey. We investigated the 3D velocity and spatial structures of the molecular component of massive outflows at milli-arcsecond angular resolution using multi-epoch Very Long Baseline Array (VLBA) observations of 22 GHz water masers. We also characterize the ionized component of the flows using deep images of the radio continuum emission with resolutions of ∼0. 2, at 6, 13, and 22 GHz with the Jansky Very Large Array (JVLA). Results. We report the first results obtained for a subset of 11 objects from the sample. The water maser measurements provide us with a very accurate description of the molecular gas kinematics. This in turn enables us to estimate the momentum rate of individual outflows, varying in the range 10 −3 -10 0 M yr −1 km s −1 , among the highest values reported in the literature. In all the observed objects, the continuum emission at 13 and 22 GHz has a compact structure, with its position coincident with that of the water masers. The 6 GHz continuum consists of either compact components (mostly well aligned with the 13 and/or 22 GHz sources) or extended emission (either highly elongated or approximately spherical), which can be offset by up to a few arcseconds from the water masers. The unresolved continuum emission associated with the water masers likely points to the YSO location. The comparison of the radio continuum morphology to the maser spatial and 3D velocity distribution shows that five out of eleven high-mass YSOs emit a collimated outflow, with a flow semi-opening angle in the range 10• -30• . The remaining six sources present a more complicated relationship between the geometry of the radio continuum and water maser velocity pattern; therefore, no firm conclusions can be drawn regarding their outflow structure. In two sources, the 6 GHz continuum emission shows a highly elongated structure with a negative spectral index down to −1.2. We interpret this finding in terms of synchrotron emission from relativistic electrons accelerated in strong shocks, which indicates that non-thermal continuum emission could be common in high-mass protostellar jets. The Lyman continua derived from bolometric luminosities always exceed those obtained from the radio luminosities. Conclusions. These first results suggest that collimated outflows or jets can be common in high-mass YSOs and, in a couple of cases, provide hints that magnetic fields could be important in driving ...
Context. In high-mass (≥7 M ) star formation (SF) studies, high-angular resolution is crucial for resolving individual protostellar outflows (and possibly accretion disks) from the complex contribution of nearby (high-and low-mass) young stellar objects (YSO). Previous interferometric studies have focused mainly on single objects. Aims. A sensitive survey at high angular resolution is required to investigate outflow processes in a statistically significant sample of high-mass YSOs and on spatial scales relevant to testing theories. Methods. We selected a sample of 40 high-mass YSOs from water masers observed within the BeSSeL Survey. We investigated the 3D velocity and spatial structures of the molecular component of massive outflows at milli-arcsecond angular resolution using multi-epoch Very Long Baseline Array (VLBA) observations of 22 GHz water masers. We also characterize the ionized component of the flows using deep images of the radio continuum emission with resolutions of ∼0. 2, at 6, 13, and 22 GHz with the Jansky Very Large Array (JVLA). Results. We report the first results obtained for a subset of 11 objects from the sample. The water maser measurements provide us with a very accurate description of the molecular gas kinematics. This in turn enables us to estimate the momentum rate of individual outflows, varying in the range 10 −3 -10 0 M yr −1 km s −1 , among the highest values reported in the literature. In all the observed objects, the continuum emission at 13 and 22 GHz has a compact structure, with its position coincident with that of the water masers. The 6 GHz continuum consists of either compact components (mostly well aligned with the 13 and/or 22 GHz sources) or extended emission (either highly elongated or approximately spherical), which can be offset by up to a few arcseconds from the water masers. The unresolved continuum emission associated with the water masers likely points to the YSO location. The comparison of the radio continuum morphology to the maser spatial and 3D velocity distribution shows that five out of eleven high-mass YSOs emit a collimated outflow, with a flow semi-opening angle in the range 10• -30• . The remaining six sources present a more complicated relationship between the geometry of the radio continuum and water maser velocity pattern; therefore, no firm conclusions can be drawn regarding their outflow structure. In two sources, the 6 GHz continuum emission shows a highly elongated structure with a negative spectral index down to −1.2. We interpret this finding in terms of synchrotron emission from relativistic electrons accelerated in strong shocks, which indicates that non-thermal continuum emission could be common in high-mass protostellar jets. The Lyman continua derived from bolometric luminosities always exceed those obtained from the radio luminosities. Conclusions. These first results suggest that collimated outflows or jets can be common in high-mass YSOs and, in a couple of cases, provide hints that magnetic fields could be important in driving ...
From measuring the annual parallax of water masers over one and a half years with VERA, we present the trigonometric parallax and corresponding distance of another newly identified water maser source in the region of IRAS 20231+3440 as π = 0.611 ± 0.022 mas and D = 1.64 ± 0.06 kpc respectively. We measured the absolute proper motions of all the newly detected maser spots (30 spots) and presented two pictures describing the possible spatial distribution of the water maser as the morphology marks out an arc of masers whose average proper motion velocity in the jet direction was 14.26 km s −1 . As revealed by the ALLWISE composite image, and by applying the colour-colour method of YSO identification and classification on photometric archived data, we identified the driving source of the north maser group to be a class I, young stellar object. To further probe the nature of the progenitor, we used the momentum rate maximum value (1.2×10 −4 M yr −1 km s −1 ) of the outflow to satisfy that the progenitor under investigation is a low mass young stellar object concurrently forming alongside an intermediate-mass YSO ∼ 60, 000 au (∼ 37 arcsecs) away from it.
We have performed an unbiased search for outflows from young stars in Cygnus-X using 42 deg 2 of data from the UKIRT Widefield Infrared Survey for H 2 (UWISH2 survey), to identify shock-excited near-IR H 2 emission in the 1 -0 S(1) 2.122 µm line. We uncovered 572 outflows, of which 465 are new discoveries, increasing the number of known objects by more than 430 %. This large and unbiased sample allows us to statistically determine the typical properties of outflows from young stars.We found 261 bipolar outflows and 16 % of these are parsec-scale. The typical bipolar outflow is 0.45 pc in length and has gaps of 0.025 to 0.1 pc between large knots. The median luminosity in the 1 -0 S(1) line is 10 −3 L . The bipolar flows are typically asymmetrical, with the two lobes misaligned by 5 • , one lobe 30 % shorter than the other, and one lobe twice as bright as the other. Of the remaining outflows, 152 are singlesided and 159 are groups of extended, shock-excited H 2 emission without identifiable driving sources. Half of all driving sources have sufficient WISE data to determine their evolutionary status as either protostars (80 %) or classical T-Tauri stars (20 %). One fifth of the driving sources are variable by more than 0.5 mag in the K-band continuum over several years.Several of the newly-identified outflows provide excellent targets for follow up studies. We particularly encourage the study of the outflows and young stars identified in a bright-rimmed cloud near IRAS 20294+4255, which seems to represent a textbook example of triggered star formation.
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